Effects of prolonged high-altitude exposure on peripheral adrenergic receptors in young healthy volunteers

The regulation of adrenergic receptors during hypoxia is complex, and the results of published reports have not been consistent. In the present study blood cell adrenoceptor characteristics at sea level (SL) before and after prolonged exposure to high altitude (HA) were measured in seven trained young male lowlanders. Sympathoadrenal activity and clinical haemodynamic parameters were also evaluated before departure (SLB), after 1 week (HA1) and 4 weeks (HA4) at HA and 1 week after return to sea level (SLA). As compared to pre-departure sea level values, urinary norepinephrine excretion increased significantly during altitude exposure [SLB: 10.26 (3.04) μg · 3 h⁻¹; HA1: 23.2 (4.19) μg · 3 h⁻¹; HA4: 20.3 (8.68) μg · 3 h⁻¹] and fell to pre-ascent values 1 week after return to sea level [SLA: 9 (2.91) μg · 3 h⁻¹]. In contrast, mean urinary epinephrine levels did not increase over time at HA. Both systolic and diastolic blood pressures, as well as heart rate, were increased during HA exposure. The circadian blood pressure and heart rate rhythms were preserved during all phases of altitude exposure. Mean maximal binding (B _max) of the α₂-adrenoceptor antagonist [³H]rauwolscine to platelet membranes was significantly reduced (P < 0.001) after exposure to chronic hypoxia [SLB: 172.6 (48.5) fmol · mg⁻¹ protein versus SLA: 136.8 (56.1) fmol · mg⁻¹ protein] without change in the dissociation constant (K _D). Neither the lymphomonocyte β₂-adrenoceptor B _max [SLB: 38.5 (13.6) fmol · mg⁻¹ protein, versus SLA: 32.4 (12.1) fmol · mg⁻¹ protein] nor the K _D for [³H]dihydroalprenolol was affected by chronic hypoxia. Cyclic AMP (adenosine 3′,5′-cyclic monophoshate) generation in lymphomonocytes by maximal isoproterenol stimulation was not modified after prolonged HA exposure. In conclusion, the down-regulation of α₂-adrenoceptors appears to be an important component of the adrenergic system response to HA exposure. Accepted: 20 April 2000     

Effects of breathing control on cardiocirculatory modulation in Caucasian lowlanders and Himalayan Sherpas

This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude in adapted and non-adapted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on synchronized 15 min periods of R-R intervals and the oxygen saturation of arterial blood (S_aO₂). Despite mean S_aO₂ being similar in lowlanders and Himalayan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], fluctuations in S_aO₂ were significantly increased in lowlanders compared to Sherpas, thus indicating an unstable regulation of respiration control in lowlanders. Regression analysis demonstrated a significant relationship between spectrum power of S_aO₂ and the relative power of R-R intervals in the frequency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas. Our results demonstrate differences in respiratory and autonomic cardiac control between non-adapted lowlanders and Himalayan high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated with the autonomic cardiocirculatory regulation. Accepted: 11 September 2000     

Chemoreceptor drives and short sleep-wake cycles during hypoxia: A simulation study

We used a Grodins-type mathematical model of the cardio-pulmonary system to investigate the cycling behaviour of the respiratory system during hypoxia in response to changes of state between waking and sleeping, namely a diminution of respiratory chemosensitivity during sleep. Shifts between waking and sleeping were triggered by various combinations of threshold values for PAO₂. Mild or moderate hypoxia was simulated by values of inspired O₂ concentration between 13% and 16% (normal 21%). In mild or moderate hypoxia, reductions of overall respiratory gain from about 2 to 0.8 l·min⁻¹ mmHg⁻¹ at sleep onset will produce falls in PAO₂ likely to cause sleep-wake cycles with oscillations in PAO₂. The higher the arousal threshold (in relation to steady-state PAO₂ during sleep), the shorter and more stable the sleep-wake cycles. As the arousal threshold is raised, and as hypoxia is exacerbated from mild (FIO2=16%) to moderate (FIO2=13%), the sleep-wake cycle length tends to converge to a value around one minute. The level and determinants of the “back-to-sleep” threshold are hard to define from presently available experimental data, but the level is not important in determining the length of the sleep-wake cycle compared to the arousal threshold. Alinearities in chemoreceptor feedback were introduced first by incorporating “drive” thresholds, to simulate central or obstructive apnoea. This produced larger oscillations in respiratory variables, but no change in cycle length. Chemoreceptor thresholds for PCO₂ at the level of 38–39 mmHg did produce shorter ventilation cycles, down to about 20 s in length, but these were not related in any simple way to the resulting sleep-wake cycles. The combination of sleep state changes and chemoreceptor feedback alinearities can produce short sleep-wake cycles despite the diminution in chemoreceptor gain occurring in sleep.     

Detecting natural selection in high-altitude human populations

High-altitude natives have distinctive biological characteristics that appear to offset the stress of hypoxia. Evolutionary theory reasons that they reflect genetic adaptations resulting from natural selection on traits with heritable variation. Furthermore, high-altitude natives of the Andean and Tibetan Plateaus differ from one another, perhaps resulting from different evolutionary histories. Three approaches have developed a case for the possibility of population genetic differences: comparing means of classical physiological traits measured in samples of natives and migrants between altitudes, estimating genetic variance using statistical genetics techniques, and comparing features of species with different evolutionary histories. Tibetans have an inferred autosomal dominant major gene for high oxygen saturation that is associated with higher offspring survival, a strong indicator of ongoing natural selection. New approaches use candidate gene and genomic analyses. Conclusive evidence about population genetic differences and associations with phenotypes remains to be discovered.     

Promotion of sleep by heat in young rats

The aim of the experiments was to study the effects of a moderate heat load on sleep in young (26-day-old) rats and to determine whether the sleep-promoting effect of heat results from stimulation of the homeostatic sleep process. The changes in sleep-wake activity, electroencephalogram slow wave activity (SWA) during non-rapid eye movement sleep (NREMS) and cortical temperature (T _crt) were determined during and after long (24-h) and short (2.5-h) heat loads (elevation of ambient temperature from 26° C to 32° C), and after total sleep deprivation (SD) combined with a short-term heat load. The heat exposures elicited increases in T _crt and rectal temperature (2 and 1.7° C respectively). The long-term heat load induced persistent, albeit slight enhancements in NREMS. Rapid eye movement sleep (REMS) increased with a 12-h delay during the 24-h heat load. Heat elicited an immediate large increase in SWA. After this initial increase, SWA declined and tended to fall below the baseline level during the last 12 h of the 24-h heat load. SWA and REMS were significantly suppressed after termination of 24-h heat loading. The increased SWA during the short-term heat load was not followed by subsequent alterations in sleep when the ambient temperature had returned to normal. However, after the combination of SD with the shortterm heat load the durations of NREMS and SWA were significantly enhanced compared with those found after SD at 26° C. The results are interpreted as suggesting that heat increases NREMS in the young rat by the same mechanism as is involved in the enhancement of NREMS after SD: a stimulation of sleep drive.     

基因组学研究在藏族高原适应遗传机制研究中的实践与运用

世居高原藏族在长期的高原低氧适应过程中,其多项生理特征显著不同于世居平原民族,这些指标变化可能与特殊环境所导致的基因组序列变异相关.近年来随着高通量测序以及全基因组关联分析等新型研究平台的迅猛发展,它们广泛应用到藏族高原适应的遗传机制的研究中.此文就基因组学领域藏族高原适应的遗传机制进展进行综述,为进一步探索高原适应机制和高原病发病机制提供参考,并为高原病的防治寻找新的思路和靶点.     

468例癫癎患者睡眠期癎样放电与睡眠结构变化分析

目的：观察癫 患者的睡眠时相与 样放电的关系,并初步探讨癫 异常脑波活动对睡眠的影响。方法：对４６８例癫　患者进行２４小时动态脑电图（ＡＥＥＧ）监测,观察发作间期清醒与睡眠脑电图　样放电的发作频率,分析５８例癫　患者及对照组睡眠脑电图中睡眠时程、觉醒次数、睡眠纺锤波的变化。结果：４６８例患者中出现　样放电３６２例,睡眠期　样放电检出率８８％,觉醒期检出率５８％。样放电主要出现于ＮＲＥＭ睡眠Ⅰ－Ⅱ期。与对照组比较,癫　组ＮＲＥＭ　Ⅰ－Ⅱ睡眠期延长,ＮＲＥＭ Ⅲ－Ⅳ期缩短;觉醒次数增加,觉醒次数与　样放电频率呈正相关;并有睡眠纺锤波减少及不对称。结论：癫　患者的　样放电主要出现于ＮＲＥＭ睡眠Ⅰ－Ⅱ期,癫　活动对睡眠有一定影响,癫　患者睡眠质量下降。     

成年Sprague-Dawley大鼠的睡眠结构和呼吸暂停分析

目的：了解成年Sprague-Dawley大鼠生理状态下的睡眠结构以及清醒/睡眠状态下的呼吸暂停情况。方法：对每只SD大鼠进行6 h的睡眠呼吸监测。大鼠的皮质脑电、颈部肌电以及通过微压传感器记录到的呼吸信号经过多导生理仪放大，以波形形式在计算机上同步显示并储存。使用人机交互的方法进行脑电分期和呼吸暂停的判断。SAS软件分析数据。结果：26只成年雄性SD大鼠的非快动眼睡眠期(NREM)和快动眼睡眠期(REM)分别占总睡眠时间的(83.3±7.1)%和(16.2±7.1)%。全部监测大鼠在睡眠中出现呼吸暂停，平均睡眠呼吸暂停指数(AI)为(11.5±4.6)次/h。其中REM期的呼吸暂停最频繁。且叹息后呼吸暂停主要发生于NREM期，而自发呼吸暂停主要发生于REM期。结论：成年SD大鼠具有与人类相似的睡眠结构，睡眠中发生的中枢性呼吸暂停现象及其表现特点也与人类SAS患者相似，可以作为研究睡眠呼吸暂停中枢发病机制的天然动物模型。     

Unbiased categorical classification of pediatric sleep disordered breathing

Study Objectives:

To classify pediatric sleep disordered breathing (SDB) using unbiased approaches. In children, decisions regarding severity and treatment of SDB are conducted solely based on empirical observations. Although recognizable entities clearly exist under the SDB spectrum, neither the number of SDB categories nor their specific criteria have been critically defined.

Design:

retrospective cohort analysis and random prospective cohort

Setting:

community and clinical sample

Patients or Participants:

Urban 5- to 9-year-old community children undergoing overnight sleep study (NPSG), and a comparable prospectively recruited clinical SDB sample.

Interventions:

n/a

Measurements and Results:

Principal component analysis was used to identify the uniqueness of the polysomnographically derived measures that are routinely used in clinical settings: apnea-hypopnea index, apnea index, obstructive apnea index, nadir SpO₂, spontaneous arousal index and respiratory arousal index. These measures were then incorporated using unbiased data mining approaches to further characterize and discriminate across categorical phenotypes. Of 1,133 subjects, 52.8% were habitual snorers. Six categorical phenotypes clustered without any a priori hypothesis. Secondly, a non-hierarchical model that incorporated 6 NPSG-derived measures enabled unbiased identification of algorithms that predicted these 6 severity-based clusters. Thirdly, a hierarchical model was developed and performed well on all severity-based clusters. Classification and predictive models were subsequently cross-validated statistically as well as clinically, using 2 additional datasets that included 259 subjects. Modeling reached ∼93% accuracy in cluster assignment.

Conclusions:

Data-driven analysis of conventional NPSG-derived indices identified 6 distinct clusters ranging from a cluster with normal indices toward clusters with more abnormal indices. Categorical assignment of individual cases to any of such clusters can be accurately predicted using a simple algorithm. These clusters may further enable prospective unbiased characterization of clinical outcomes and of genotype-phenotype interactions across multiple datasets.

Citation:

Spruyt K; Verleye G; Gozal D. Unbiased categorical classification of pediatric sleep disordered breathing. SLEEP 2010;33(10):1341-1347.     

高海拔地区儿童急性呼吸衰竭的微循环变化

本文报告高海拔地区急性呼吸衰竭患儿37例，在入院24小时内进行甲襞微循环视察，并与正常组进行对比研究。结果表明；甲襞微循环的血管形态、血流状态、襻周状态等多项指标有明显改变，输入枝明显收缩变细，输出枝随缺氧程度加重变宽。血流速度减慢、血流摆动、停滞，红细胞聚集，襻周出血、渗出等改变使微循环正常流态发生紊乱。这些可能是构成儿童急性呼吸衰竭微循环障碍的病理学基础。     

Severe gastritis in the Peruvian Andes

OBJECTIVE: To compare the Helicobacter pylori-associated pathology in gastric biopsies taken from patients living at sea level with those taken from patients living at high altitude. METHODS AND RESULTS: We included 38 patients from a hospital in the Andean city of La Oroya, Peru, located at 3700 m in altitude, and 40 control patients taken from Comas Clinic located in the city of Lima at sea level. Fibrepanendoscopy and multiple biopsies were performed in all the patients followed by histopathological examination. In the antrum, patients from the Andean town had a higher prevalence of glandular lymphoid adherence lesions, active germinal centres, moderate to severe chronic atrophic gastritis, intestinal metaplasia and moderate to severe total deep gland loss, than did patients from the coastal town. Furthermore, the severity of the histological lesions seen in the gastric body and cardia was significantly greater in the high-altitude patients than in those from sea level. CONCLUSION: This study suggests that the severity of H. pylori-associated gastric lesions seen on histopathological examination is greater in patients living at high altitude, the cause of which is most probably multifactorial but nonetheless principally altitude related.     

Topography of age-related changes in sleep spindles

Aging induces multiple changes to sleep spindles, which may hinder their alleged functional role in memory and sleep protection mechanisms. Brain aging in specific cortical regions could affect the neural networks underlying spindle generation, yet the topography of these age-related changes is currently unknown. In the present study, we analyzed spindle characteristics in 114 healthy volunteers aged between 20 and 73 years over 5 anteroposterior electroencephalography scalp derivations. Spindle density, amplitude, and duration were higher in young subjects than in middle-aged and elderly subjects in all derivations, but the topography of age effects differed drastically. Age-related decline in density and amplitude was more prominent in anterior derivations, whereas duration showed a posterior prominence. Age groups did not differ in all-night spindle frequency for any derivation. These results show that age-related changes in sleep spindles follow distinct topographical patterns that are specific to each spindle characteristic. This topographical specificity may provide a useful biomarker to localize age-sensitive changes in underlying neural systems during normal and pathological aging.     

Respiratory function and blood gas variables in cystic fibrosis patients during reduced environmental pressure

Patients with cystic fibrosis (CF) suffer from hypoxaemia even under normobaric conditions and the reduction of inspiratory PO₂ (O₂ partial pressure) during air travel corresponding to an altitude of 1,800–2,450 m might be a problem for these patients. Ten CF patients and 27 healthy control subjects were investigated in a chamber where the ambient pressure was reduced to that found at 2,000 and 3,000 m. The respiratory function was reduced in the CF patients with a vital capacity of 3.1 (0.3) l [vs 4.9 (0.2) l in controls; mean (SEM)] and a forced expiratory 1-s volume of 2.1 (0.3) l [vs 4.3 (0.20 l in controls], unrelated to the reduction in ambient pressure. Mean arterial PO₂ decreased from 75 (4) mmHg [85 (1) mmHg in controls, P<0.01] at sea level to 58 (3) mmHg at 580 mmHg and to 46 (1) mmHg [58 (1) mmHg and 49 (2) mmHg in controls, n.s.] at 513 mmHg ambient pressure. These results indicate that during air travel with a cabin pressure that corresponds to an altitude of 2,500 m, the arterial PO₂ of CF patients is likely to remain above the accepted critical value of 50 mmHg. However, a further reduction of the pressure to that found at 3,000 m altitude may lead to severe hypoxia in patients with moderate airway obstruction.     

High‐altitude hypoxia and periodic breathing during sleep: gender‐related differences

High‐altitude exposure is characterized by the appearance of periodic breathing during sleep. Only limited evidence is available, however, on the presence of gender‐related differences in this breathing pattern. In 37 healthy subjects, 23 male and 14 female, we performed nocturnal cardio‐respiratory monitoring in the following conditions: (1) sea level; (2) first/second night at an altitude of 3400 m; (3) first/second night at an altitude of 5400 m and after a 10 day sojourn at 5400 m. At sea level, a normal breathing pattern was observed in all subjects throughout the night. At 3400 m the apnea–hypopnea index was 40.3 ± 33.0 in males (central apneas 77.6%, central hypopneas 22.4%) and 2.4 ± 2.8 in females (central apneas 58.2%, central hypopneas 41.8%; P < 0.01). During the first recording at 5400 m, the apnea–hypopnea index was 87.5 ± 35.7 in males (central apneas 60.0%, central hypopneas 40.0%) and 41.1 ± 44.0 in females (central apneas 73.2%, central hypopneas 26.8%; P < 0.01), again with a higher frequency of central events in males as seen at lower altitude. Similar results were observed after 10 days. With increasing altitude, there was also a progressive reduction in respiratory cycle length during central apneas in males (26.9 ± 3.4 s at 3400 m and 22.6 ± 3.7 s at 5400 m). Females, who displayed a significant number of central apneas only at the highest reached altitude, were characterized by longer cycle length than males at similar altitude (30.1 ± 5.8 s at 5400 m). In conclusion, at high altitude, nocturnal periodic breathing affects males more than females. Females started to present a significant number of central sleep apneas only at the highest reached altitude. After 10 days at 5400 m gender differences in the apnea–hypopnea index similar to those observed after acute exposure were still observed, accompanied by differences in respiratory cycle length.     

The effect of a high calory diet on hormonal changes in young men during prolonged physical strain and sleep deprivation

Summary Major changes occur in the serum level of several hormones during 5 days of heavy and continuous physical activities, with less than a total of 2 h of sleep. The present investigation was designed to evaluate the importance of caloric deficiency, energy requirement being about 8,000–10,000 kcal/24 h. A comparison between well fed subjects and those with food deprivation revealed significantly higher levels of (T₃) triiodothyronin, insulin and thyroid stimulating hormone (TSH) in the well-fed subjects, who also had lower levels of growth hormone (hGH) and cortisol, whereas no difference was found between the two groups for thyroxin (T₄). Increased levels were found for T₃ and T₄ in both groups during the first day of activity, with a concomitant decrease in TSH and a subsequent decrease of T₄ during the next 2 days. T₃ decreased only in the low-calory group whereas increased levels were found in the iso-calory group throughout the course. The resting levels of insulin decreased during the course in the low-calory group whereas it increased in the iso-calory group. High levels were maintained throughout the course for hGH. Cortisol showed high levels just before the start of the course and then decreased from day 2 to day 4. No difference was found between the morning and evening levels for cortisol, indicating disappearance of the circadian rhythm. The present investigation has shown that energy deficiency during prolonged physical strain is responsible for the decreased serum levels of T₃ and insulin and may contribute to the decrease in TSH and the increase in hGH and cortisol.     

EEG delta power during sleep in young and old rats

Delta EEG power density, which has been viewed as a measure of intensity of NREM sleep, declines across the lifetime in humans, cats, and hamsters, but data in rats have been unclear. It is also uncertain whether older rats differ from younger animals in the degree of change in delta power during recovery sleep following short-term sleep deprivation. We have examined delta power density in NREM sleep under baseline conditions and following 48 h of sleep deprivation in young (3 months), middle-aged (12 months), and older (24 months) rats. The presence or absence of age effects was highly dependent on the method of normalizing the data. When expressed as a fraction of total NREM EEG power, there was no age effect on baseline delta power density, or on the change from baseline to recovery conditions. When expressed as a multiple of delta power in REM under the same condition, the younger rats had higher delta power density than the middle-aged and older rats. For all the ages combined, there was an increase in delta power density in the recovery condition. When examined by age, the younger rats (which started from a higher level of delta power density than the other groups) did not have an increase in delta during recovery; the middle-aged rats tended to, and the older rats (which started from lower baseline levels) significantly increased delta power density in the recovery condition. This suggests that the lower delta power seen during baseline in older rats is not due to decreased ability to generate delta activity.     

Respiratory sinus arrhythmia during sleep in children with upper airway obstruction

Upper airway obstruction during adulthood is associated with cardiovascular morbidity; cardiovascular consequences of childhood upper airway obstruction are less well established. This study aimed at investigating the effect of childhood upper airway obstruction on respiratory sinus arrhythmia as a measure of cardiac vagal modulation during night‐time sleep. Overnight polysomnography was conducted in 40 healthy children (20 M; age: 7.5 ± 2.6 years; body mass index percentile: 60.7 ± 26.4%) and 40 children with upper airway obstruction (24 M; age: 7.5 ± 2.7 years; body mass index percentile: 65.8 ± 31.9%). We used the phase‐averaging technique to compute respiratory sinus arrhythmia amplitude and phase delay. To study sleep stage effects and the effect of upper airway obstruction, respiratory sinus arrhythmia was measured during all artefact‐free sleep episodes, and after exclusion of respiratory events. A significant increase in respiratory sinus arrhythmia amplitude and phase delay was observed during stage 4 sleep as compared with rapid eye movement sleep in both groups (amplitude: controls = 0.10 ± 0.03 versus 0.07 ± 0.02 s, P < 0.01, respectively, and upper airway obstruction = 0.07 ± 0.03 versus 0.05 ± 0.03 s, P < 0.05, respectively; phase delay: controls = 3.1 ± 0.1 versus 3.0 ± 0.1 rad, P < 0.05, respectively, and upper airway obstruction = 3.13 ± 0.04 versus 3.04 ± 0.08 rad, P < 0.01, respectively). A significant association between respiratory sinus arrhythmia and apnea/hypopnea index was observed during stage 2 sleep in children with upper airway obstruction. Compared with healthy controls, a significant decrease in respiratory sinus arrhythmia amplitude during stage 2 sleep was observed in children with upper airway obstruction (0.09 ± 0.03 versus 0.06 ± 0.03 s, P < 0.05). However, this difference was not apparent when respiratory events were excluded from analysis. Importantly, respiratory sinus arrhythmia showed a strong negative correlation with body mass index. In conclusion, night‐time respiratory sinus arrhythmia in children is sleep stage dependent and normal during quiet sleep in children with relatively mild upper airway obstruction.     

Age-related changes in sleep in inbred mice are genotype dependent

Aging produces major changes in sleep structure and intensity which might be linked to cognitive impairment in the elderly. In this study, the genetic contribution to age-related changes in sleep was assessed in three inbred mouse strains of various ages. Baseline sleep and the response to 6 hours sleep deprivation (SD) achieved by gentle handling were quantified in young, middle-aged, and older male mice using electroencephalography. Total sleep time initially increased with age but then decreased in the oldest group mainly due to changes in sleep duration during the active phase. The effect of age on electroencephalographic (EEG) delta power depends on genotype and sleep pressure level with SD increasing the age-related differences. The strong effect of age upon the spectral profile of the different behavioral states was modulated by genetic background. Overall, our results suggest that sleep pressure can modulate the effect of age, that most sleep variables do not monotonically change with age in contrast to previous reports in humans and other species, and that genetic factors have a major impact on the aging processes affecting sleep.     

Improved physical fitness failed to alter the EEG patterns of sleep in young women

Summary We investigated the effect of a 12-week physical training programme on the sleep of nine unfit women. Data were collected at 0, 4, 8 and 12 weeks of the training programme. Changes in fitness were assessed by changes in maximal oxygen consumption ( ) and onset of blood lactate turn point (LTP). Lean body mass (LBM) was calculated from total body potassium measurements. The all-night sleep recordings were made following days during which the subjects carried out their normal daily routines and did no extra exercise. Although cardiorespiratory fitness improved significantly as indicated by an increase in both and LTP, there was no change in LBM. The improvement in cardiorespiratory fitness did not result in any changes in the sleep parameters measured. Other workers have reported an improvement in sleep quality in eight army recruits during their basic training. The male recruits showed improved cardiorespiratory fitness and an increase in muscle bulk. These results suggest that increased fitness only facilitates sleep when there is an associated increase in LBM. Alternatively it may be that the response of sleep to improved fitness is sex-linked.     

ERP and behavioral changes during the wake/sleep transition

Event-related potentials (ERPs) following infrequent and frequent stimuli were studied as subjects moved from wakefulness to sleep. Subjects were instructed to respond to the infrequent “target” stimuli (attend condition) or to ignore the stimuli (ignore condition). Parietal P300, prominent following target ERPs in wakefulness under the attend condition, disappeared in association with reduced behavioral responsiveness and emergence of a central negativity (N350). The N350 and preceding and following positivities (P220 and P450) became the dominant feature of both target and nontarget ERPs under both attend and ignore conditions. The P220-N350-P450 complex was larger and peak latencies were shorter under the attend condition. Peak amplitudes tended to be larger following targets, especially under the attend condition. The findings suggest that, although the processes under-lying P300 are less likely to be engaged, processing of stimulus deviance and task relevance continues in sleepiness and sleep, and is reflected by variance in N350 and related activity.